Forging uses intense heat and pressure to transform a [solid}
slug of alloy material into the final shape of a wheel. Forged
aluminium is about 300 per cent stronger than cast aluminium, yet
less material is needed to produce the same "cast alloy wheel",
which results in a lighter product. Because of the basic
limitations inherent in forging, most forged wheels are two or
three piece units. In two-piece construction, a centre is forged
and welded or bolted into a spun or stamped outer rim. In a
three-piece wheel, the centre is bolted to an inner and an outer
rim half. This stands as an advantage of being easily customisable
for a variety of widths and offsets.
Casting is a relatively inexpensive way to produce a high-quality,
fairly strong alloy wheel. There are two methods used. One, system
is known as gravity casting... whereby the molten material is
poured into a mold and allowed to cool. These molds are usually
made by machining a piece of material on CNC machine equipments to
produce a wheel that only requires minor finishing (like drilling
or possibly trimming of some excess metal) to be considered
complete. The other and better system used is the low pressure or
negative pressure casting. Here instead of pouring the molten
material into the mould, the molten alloy is drawn up into the
mould using a high-pressure vacuum. This eliminates much of the
trapped air found in gravity casting process, producing a stronger
wheel that is less porous than a gravity-cast one.
